A DNS resolver cache is a temporary storage location on a machine, either within the operating system (OS) or a web browser, that holds information about previous DNS lookups.
Understanding the DNS Resolver Cache
At its core, a DNS resolver cache is like a local address book for websites you've recently visited. Instead of asking a distant DNS server for a website's IP address every single time you want to access it, your machine first checks this local cache.
As the reference states, the DNS cache refers to the temporary storage of information about previous DNS lookups on a machine's OS or web browser. This local copy allows your system or browser to bypass the standard DNS resolution process for known entries.
How it Works
When you type a website address (like www.example.com) into your browser, your computer needs to find the numerical IP address associated with that name. This is typically done through the Domain Name System (DNS).
- Check Cache: The first step is to check the local DNS resolver cache.
- Cache Hit: If the mapping of
www.example.comto its IP address is found in the cache (a "cache hit"), the system uses the cached information directly. - Cache Miss: If the information is not in the cache (a "cache miss"), the system proceeds to perform a standard DNS lookup using external DNS servers.
- Store Result: Once the IP address is obtained from external servers, it is then stored in the local DNS cache for future use, usually for a specific duration known as the Time-To-Live (TTL).
Where DNS Caches Reside
DNS caches exist at several levels on your machine and network:
- Operating System (OS) Cache: Your computer's operating system maintains its own DNS cache. This is used by all applications on the system.
- Web Browser Cache: Most web browsers also maintain their own DNS caches, which can sometimes override or supplement the OS cache for requests made through that specific browser.
Why it Matters: Benefits
Keeping this local copy offers significant advantages:
- Efficiency and Speed: As highlighted in the reference, keeping a local copy of a DNS lookup allows your OS or browser to quickly retrieve it and thus a website's URL can be resolved to its corresponding IP much more efficiently. This means websites load faster because the time-consuming external DNS lookup is skipped.
- Reduced Network Traffic: It decreases the number of requests sent to external DNS servers, reducing network load.
- Improved User Experience: Faster resolution contributes to a smoother and quicker browsing experience.
Practical Aspects
The data in the cache is temporary and subject to the TTL value provided by the DNS record. When the TTL expires, the cached entry is removed, and a new lookup will be performed the next time the domain is requested.
Clearing your DNS cache is a common troubleshooting step when you encounter issues accessing a website, especially if its IP address has recently changed.
